This invention relates to a process and apparatus for embossing the internal surface of heat exchanger tubing to produce ribs or grooves thereon.
In the tubing of an air conditioner condenser coil, evaporator coil, or other heat exchanger, it is preferred that the inner surfaces of the tube be provided with ribs or the like to increase its surface area and to increase the efficiency in condensing or evaporating a refrigerant fluid.
A machine for grooving or embossing the inner surface of heat exchanger tubing, which can be a copper pipe, is conventionally constructed by combining a more-or-less standard tube drawing machine with a draw bench, an outer doughnut-type die, and an inner die having a grooved surface which produces the rib enhancement on the pipe inner surface. A plurality of rollers or balls rotate planetarily, that is, in a circumferential direction, around the part of the pipe where the grooving die is positioned.
There is normally a tremendous stress in the pipe caused by the compression of the tube by contacting of the rolls with the internal die. This is compounded by the small contact area, which requires small leads to be employed. Processing speed is affected, which therefore must be undesirably low. This raises the cost of processing the copper pipe.
An embossing machine which employs planetarily rotating balls for sinking the tubing into the internal die are contained in a head that rotates coaxially with the pipe or tube. One such construction is described in U.S. Pat. No. 4,373,366.
It should be noted that that embossing machine, because of the generally circumferential motion of the ball-type pressing members, is suitable for producing spiral or helical bosses, but seems less adequate for axial internal grooves, fluting, or ribs. Also, whether or not desired, there are spiral grooves produced on the outer surface of the tube due to the generally spiral motion of the balls.
It is desired to replace the conventional process of tube sinking onto an internal die or mandrel. More particularly, it is desired to replace the conventional rotary die with a plurality of rotating die members which roll into contact with the tube in a direction parallel to the movement of the tube.